Thomas Aquinas

“ If, therefore, after consenting to marry a woman by words expressive of the future and confirming that consent with an oath, a man binds himself to another woman by words expressive of the present, it would seem that none the less he is bound to keep his former oath. But this would not be the case unless that oath made the marriage complete. Therefore an oath affixed to a consent expressed in words of the future tense makes a marriage. ”

“ In a case of this kind the affianced husband, before his marriage with the other woman, is bound to marry the one to whom he was betrothed, if she be his equal or superior in rank. But if he has married another woman, he is no longer able to fulfill his obligation, wherefore it suffices if he provide for her marriage. ”

“ Secondly, in reference to the judgment of the Church; and since in the external tribunal judgment is given in accordance with external evidence, and since nothing is more expressly significant of consent than carnal intercourse, it follows that in the judgment of the Church carnal intercourse following on betrothal is declared to make a marriage, unless there appear clear signs of deceit or fraud [*According to the pre-Tridentine legislation] (De sponsal. et matrim., cap. Is qui fidem) . ”